CVE-2026-72323

In the Linux kernel, the following vulnerability has been resolved:

ipv4: igmp: Fix potential UAF in igmpgqstart_timer()

A race condition exists between device teardown (inetdev_destroy) and

incoming IGMP query processing (igmp_rcv), leading to a Use-After-Free

in the IGMP timer callback.

During device destruction, inetdev_destroy() drops the primary reference

to in_device, which can drop its refcount to 0. The actual freeing of

indevice memory is deferred via RCU (using callrcu()).

Concurrently, igmp_rcv() runs under RCU read lock and obtains the

in_device pointer. Because the memory is RCU-protected, CPU-0 can safely

dereference in_device even if its refcount has hit 0.

However, if CPU-0 calls igmpgqstart_timer() and re-arms the timer, it

attempts to acquire a reference using indevhold(). This increments the

refcount from 0 to 1, triggering a "refcount_t: addition on 0" warning.

Since the in_device memory is still scheduled to be freed after the RCU

grace period (as the free callback does not check the refcount again),

the device is freed while the timer is still armed. When the timer

expires, it accesses the freed memory, causing a kernel panic.

Fix this by using refcountincnot_zero() (via a new helper

indevhold_safe()) to prevent acquiring a reference if the device is

already being destroyed. If the refcount is 0, we do not arm the timer.

A similar issue in IPv6 MLD is fixed in a subsequent patch.